Adverse Events Are Common With Medical Cannabis for Chronic Pain, but Serious Harms Are Rare | Research

The takeaway

A systematic review of 39 studies found that about 1 in 4 medical cannabis users for chronic pain experience some adverse event, but serious adverse events, cognitive problems, and dependence each occur in fewer than 1 in 20 patients.

Chronic pain patients considering medical cannabis and clinicians advising them

39 studies, 12,143 patients

What the researchers found

Overall adverse event prevalence was 26.0% (95% CI: 13.2-41.2%). Psychiatric adverse events were most common (13.5%). Serious adverse events, cognitive adverse events, accidents, injuries, and dependence/withdrawal each occurred in fewer than 5% of patients. Longer follow-up (24+ weeks) was associated with more reported adverse events than shorter studies.

Why it matters

Chronic pain patients and their clinicians need realistic information about medical cannabis side effects to make informed treatment decisions. This review provides the most comprehensive picture of what to expect: side effects are common but usually not serious.

The numbers in context

39 studies; 12,143 patients; 26.0% any adverse event; 13.5% psychiatric adverse events; <5% each for serious AEs, cognitive AEs, accidents/injuries, and dependence; longer use (24+ weeks) associated with more AEs (interaction p<0.01)

How the study worked

Systematic review and meta-analysis searching MEDLINE, EMBASE, PsycINFO, and CENTRAL. Included 39 non-randomized studies of adults or children with chronic pain using medical cannabis with at least 4 weeks of follow-up. GRADE approach used to assess certainty. Parallel guideline panel informed design.

What this study cannot tell us

All evidence rated as very low certainty due to study design limitations. Non-randomized studies are prone to confounding and selection bias. Insufficient evidence comparing medical cannabis harms to alternatives like opioids. Adverse event definitions varied across studies.

How to read the evidence

Large systematic review with meta-analysis and GRADE assessment, though underlying evidence was very low certainty

When this study was published

2022 study

The bigger picture

Medical cannabis is increasingly prescribed for chronic pain, often as an alternative to opioids. Knowing that serious harms are uncommon can help contextualize the risk-benefit calculation, though the finding that adverse events increase with longer use warrants monitoring.

Questions still open

How do medical cannabis adverse event rates compare to opioid adverse event rates? Does the increase in adverse events with longer use plateau or continue? Which cannabis formulations have the best safety profiles for chronic pain?

Common questions

How common are side effects from medical cannabis for pain?

About 1 in 4 patients experienced some adverse event, with psychiatric symptoms being most common (13.5%). However, serious adverse events occurred in fewer than 1 in 20 patients.

Does longer medical cannabis use cause more problems?

Studies with 24 or more weeks of follow-up reported significantly more adverse events than shorter studies, suggesting side effects may accumulate with continued use.

Read the original research

Long-term and serious harms of medical cannabis and cannabinoids for chronic pain: a systematic review of non-randomised studies.

BMJ open, 12(8), e054282

View on PubMed ↗Publisher’s paper ↗

Citation

Zeraatkar, Dena; Cooper, Matthew Adam; Agarwal, Arnav; Vernooij, Robin W M; Leung, Gareth; Loniewski, Kevin; Dookie, Jared E; Ahmed, Muhammad Muneeb; Hong, Brian Y; Hong, Chris; Hong, Patrick; Couban, Rachel; Agoritsas, Thomas; Busse, Jason W. (2022). Long-term and serious harms of medical cannabis and cannabinoids for chronic pain: a systematic review of non-randomised studies.. BMJ open, 12(8), e054282. https://doi.org/10.1136/bmjopen-2021-054282